It is normal to have an uneven edge with the chain 3 on the edge of a small square or an afghan. It may look lumpy, bumpy and crooked. Chain 3's may even add fullness so the sides of your afghan so they are longer than the center section of your piece. You may also find a larger gap next to the chain 3 in a crochet circle so it is not just edges that are affected by the additional fullness that the chain 3 may add.
This image shows two swatches, both crocheted with an "I" crochet hook, 8 double crochet each. The left swatch is done with the chain 3. The right swatch is done with the chain 2. Even though the measurements are close, you can see the difference in how the gaps will close up by using a chain 2 instead of a chain 3. A chain 2 will improve the final outcome of wavy edges.
There are a couple of things you can do to make edges more even or to close the gap of a circle. You can crochet a tighter chain 3 if you feel it is necessary to use a chain 3. You can also replace the chain 3 with a chain 2. The chain 2 in place of the chain 3 is a great way to reduce full edges. I have found that a chain 2 will work better and pull the edge snug, tight and even. To replace the chain 3 all you do is count your chain 2 as your first double crochet. When you get back to your other side, you do your last crochet in your previous chain 2. The objective is to eliminate the gaps and holes that the extra chain will cause.
This will also work for the half double crochet if you find that you have wavy edges or gaps in your rounds and edges. Instead of starting off with a chain 2, do a chain 1. The chain 1 will not count as your first stitch. It will just be the step to your first half double crochet allowing more control of potential wavy edges.
Any pattern is just a guide to creating a crochet piece. In the end, you are the one creating the finished project. You don't have to follow the exact instructions every time.